When I run a demo, I use two pregen heroes against the Golden Boar. One hero is good with a bow, the other with spear and shield. I start by telling the players that they are approaching the boar's cave and ask them if they want to try to ambush the boar, or try some other maneuver for advantage. Then we do a simple contest. That's when I tell them they can add a creative ability (I only let them add one in the demo). And we talk about divine favor, and what it's for.

The hero who wins the ambush contest sets the starting range of the fight, and since the heroes are good at different ranges, this puts them at odds right away. If you want, you can tell them about oaths at this point, and ask the loser if he wants to offer an oath to the winner in exchange for a better starting range.

Then we play out a few exchanges of the battle (2 or 3). Sometimes this is enough for the heroes to kill the boar, sometimes not. That demo format takes about 20 minutes to play. If you end up with a third player, give them the boar to play.

Darcy is right: don't use armor (for heroes or NPCs). Armor slows down a fight, which you don't want in a demo. If you really want to include it, you might also talk about the advanced tactic of taking actions before the battle to separate your foes from their armor.

You can hear a recording of my GenCon demo for Agon at the Sons of Kryos. I was using a Gorgon as the monster, but the format is pretty much the same as I describe here.

Maybe use Accomplishments instead to show the players how to push for what they're good at, rather than trying to pre-plan specific ability uses during the quests. Pre-planning that way will almost certainly backfire.

During quests, present the heroes with problems and situations, then demand that they come to an agreement about how to address the problem. Don't let them split up and do different things! Naturally, each player will all want to do something that uses their good abilities, and then you have good conflict between the heroes. Someone needs to step up and lead the group, probably by winning an Orate contest.